The present invention relates to an arc welding apparatus, and in particular, to a cold metal transfer (CMT) welding apparatus and method of operation.
Gas metal arc welding (GMAW), commonly referred to as metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which a consumable weld wire and a shielding gas are fed through a welding torch. There are many types of GMAW that can be used in various situations. Typically, the weld wire is fed though a contact tip made of copper or a copper alloy in the welding torch. The contact tip guides the weld wire and also provides a continuing electrical connection from a power supply to the weld wire as the weld wire is fed. The weld wire is held near or in contact with a metal welding surface such that electricity can arc between the weld wire and the surface. The arc causes a tip of the weld wire to liquefy and is subsequently applied to the welding surface. Typically, an inert or semi-inert gas is blown over the weld wire to limit contaminants near the weld. While GMAW is a useful welding technique, it can heat the welding surface to temperatures that cause undesirable material changes, such as hardening and warpage.
GMAW cold metal transfer (CMT) is a welding technique that reduces heat created on the welding surface. CMT is based on a deliberate and systematic activation and deactivation of the heating arc so as to systematically heat and cool the weld wire while bringing the wire into and out of contact with the weld pool at a rapid frequency. This is performed by axially oscillating the weld wire forward and backward through the copper contact tip with a frequency of up to 70 times per second. Unfortunately, the grinding contact between the weld wire and the contact tip can wear away the contact tip, especially if the weld wire is a harder material than the contact tip. This wearing away can cause material worn from the contact tip to be deposited on the weld wire or blown into the weld.